1. Field of the Invention
The present invention relates to a sheet processing apparatus that performs a binding process on a plurality of stacked sheet media, such as paper sheets and overhead projector (OHP) sheets, and to an image forming apparatus, such as a printer, a copying machine, and a facsimile, having such a sheet processing apparatus.
2. Description of the Related Art
Conventionally, some known image forming apparatuses include a post-processing apparatus that performs a post-process such as a binding process on a recording medium that is a sheet medium, e.g., a recording sheet, after an image is formed thereon by an image forming unit.
Such a post-processing apparatus performs a binding process by stacking a plurality of sheet-like recording media into a sheet bundle, and by driving a staple through a target position on the sheet bundle using a stapler that is a binding unit. There are some demands for the post-processing apparatus to be able to adjust such a target position on a sheet bundle more freely in this binding process. For example, the size of a sheet bundle in a width direction, which is a direction perpendicular to the conveying direction of the sheet bundle (referred to as a width direction, hereinafter), differs depending on the size of the sheet medium and the orientation in which the sheet medium is conveyed. Therefore, for example, in the two-position binding in which staples are driven through two positions on the sheet bundle in the width direction, a certain staple pitch may be appropriate for a sheet bundle having a long size in the width direction, but may appear too wide if the binding process is performed on a sheet bundle having a shorter size in the width direction. In such a case, the post-processing apparatus is required to be able to adjust the target positions on the sheet bundle more freely, and to adjust the staple pitch used in the two-position binding depending on the size of the sheet bundle in the width direction.
As a structure for satisfying such a requirement, Japanese Patent Application Laid-open No. 2000-177921, for example, discloses a post-processing apparatus that can move a stapler to a desired position of the sheet bundle in the width direction. Such a post-processing apparatus can adjust a target position on the sheet bundle in the width direction in a desired manner, and adjust the staple pitch used in the two-position binding depending on the size of the sheet bundle in the width direction.
However, such a conventional post-processing apparatus adjusts a target position on the sheet bundle by moving the stapler while keeping the sheet bundle at a fixed position. Therefore, when a member other than the stapler is arranged at a desired target position on the sheet bundle, the stapler cannot perform the binding process at the target position. Therefore, positions that can be set as a target position are restricted. For example, in a post-processing apparatus in which the sheet bundle is aligned in the conveying direction by bringing the trailing edge of a sheet medium in the conveying direction into contact with a trailing edge reference fence, and in which a binding process is performed at a target position near the trailing edge of the sheet bundle, the binding process cannot be performed on the sheet bundle at a position that is brought into contact with the trailing edge reference fence.
In the explanation above, a sheet medium on which the binding process is performed by the sheet processing apparatus is explained to be a recording sheet. However, the sheet medium is not limited to a paper sheet such as a recording sheet, and the same problem will occur when other sheet media such as OHP sheets are bundled and the binding process is performed thereon.
Furthermore, in the explanation above, the sheet processing apparatus is explained to be a post-processing apparatus that performs a post-process such as binding process on a sheet medium having a surface on which an image is formed by the image forming apparatus. However, the sheet processing apparatus is not limited to a post-processing apparatus, and the same problem will occur in any sheet processing apparatus that performs a binding process on sheet media, such as a sheet processing apparatus that is independent from the image forming apparatus.
Furthermore, a stapler is generally used as a binding unit that performs a binding process on a sheet bundle. However, the same problem will occur in a binding unit other than a stapler, such as those used in a binding process using a clip or a thread.